Cathodic activity and interfacial stability of Y0.8Ca0.2Co1-xFexO3/YSZ electrodes for solid oxide fuel cells

The Fe-doped cobaltates, Y0.8Ca0.2Co1-xFexO3-delta (x = 0.1-0.7), were prep ared and their high-temperature phase stability and cathodic activity were investigated. The perovskite/yttria-stabilized zirconia (YSZ) electrodes we re fabricated via a silk printing technique. It was found that the undoped cobaltate (x = 0) is so thermally unstable that the preparation of pure per ovskite phase was unsuccessful. The partial Fe-doping to Co (x = 0.1-0.7), however, gave us highly crystalline perovskite powders of an orthorhombic l attice. Among those samples of x = 0.1-0.7, the Y0.8Ca0.2Co0.7Fe0.3O3-delta Showed the best cathodic activity which is superior to La0.9Sr0.1MnO3. The thermal expansion coefficient of this material (10.5 X 10(-6) cm/cm-K at 2 5-1000 degrees C) was very close to that of 8 mol % YSZ (10.8 X 10(-6) cm/c m-K). As a result of interfacial reaction between Y0.8Ca0.2Co0.7Fe0.3O3-del ta and YSZ electrolyte, a spinel-type oxide was produced. But the interfaci al product formation proceeded mainly during the electrode adhesion period (1200 degrees C) whereas its growth during the cell operation (900-1000 deg rees C) was negligible. (C) 1999 The Electrochemical Society. S0013-4651(98 )08-022-7. All rights reserved.